"It is of concern naturally, but we are limited in what we can do in any prison environment," he said.

"There is no prison environment that is without risk and crime can occur in a prison just as it can out in the community."

Mr Wise said it was not practical to have every prisoner supervised when they were out of their cell.

"There are times when they are supervised, there are times when they are not," Mr Wise said.

Williams body remains at the prison and is expected to be removed later tonight.

Call for independent investigation

Williams' lawyer, Rob Stary, said his client was held in solitary confinement at the prison and the only time he came into contact with other prisoners was when he exercised.

"He was in the state's most secure prison environment; solitary confinement, supervised for every moment of every minute of every day, and whatever happened one would expect would have been supervised," he said.

He said Williams died only hours after he spoke to his client about a story in News Limited papers, which said police have paid $8,000 so Williams' daughter can attend an exclusive private school.

Mr Stary said Williams was upset about the story because it exposed his daughter to risk.

Williams was sentenced in May 2007 to a minimum of 35 years in jail for the murders of gangland rivals - father and son Lewis and Jason Moran, Mark Mallia and Michael Marshall - and conspiracy to murder Mario Condello during Melbourne's underworld war.

His father George was released from prison in June 2009 after serving a sentence for drug trafficking, while his mother Barbara was found dead in 2009 after an apparent overdose.

Williams was refused permission to attend his mother's funeral.

He leaves behind ex-wife Roberta Williams and his daughter.

'No conspiracy'

Melbourne's gangland war spawned the Underbelly books on which the popular TV series was based. Co-author of the Underbelly books, Fairfax journalist Andrew Rule, told ABC local radio he was not surprised by Carl Williams' death.

"It'll be tempting for people to speculate about that because one would wonder who stands to benefit from this. People do get assaulted in jail for very banal reasons over, you know, arguing over a packet of cigarettes or whatever," he said.

"So who's to say? Maybe he was a victim of his own publicity."

And Mr Rule says Williams' death is unlikely to reignite the gangland war.

"I think this is probably an isolated incident and I tend to guess that it may be a bit of a fluke, that it's not part of a conspiracy," he said.

"If it is part of a conspiracy, it's not one that I'd want to speculate about here because it would involve ongoing court cases. I'm not suggesting it is."

Infamous figure

In 2007, Williams made no apologies when Justice Betty King sentenced him to life for the murder of his rivals.

The man who Melbourne grew to know as the "baby-faced killer" wrote to his mother Barbara, admitting he was responsible for the loss of lives.

"Yes, I did what I did, and nothing I or anyone does will ever change that," Williams wrote in his letter.

"I am guilty of defending myself and my loved ones from being murdered - that I am.

"I am certainly not ashamed of the lengths I was forced to take to protect myself and my loved ones. I did what any man would do, if they'd been shot."

In the letters, given to Channel 7 and reprinted by The Age newspaper, Williams blamed the gangland war on a shooting at his 29th birthday.

He claimed he was shot in the stomach by the now slain Jason Moran and said from there it never stopped.

"Everyday soldiers have to kill the enemy, otherwise the enemy will kill them, and no-one calls soldiers murderers," Williams wrote.

Williams's murders of Jason Moran, his father Lewis, and of drug dealer Mallia occurred at the height of Melbourne's notorious gangland war that raged between 1998 and 2006, leaving 27 dead.

"The people I killed were far worse people than I will ever be ... I never killed or harmed any innocent people," he wrote.

"What about those who worked alongside me, whose crimes were every bit as bad as mine?

"Was it really fair, was it really justice that they got away so lightly, and in some cases without penalty at all, in exchange for my liberty?"

Williams did lament the loss of his freedom, his incarceration in solitary confinement, and missing out on seeing his daughter grow up.

"I won't be there to see her start high school. I certainly won't be there for her 21st birthday. I also doubt if I'll be there to walk her down the aisle if she gets married," he wrote.

Williams was also outraged by his portrayal as a bumbling imbecile on TV series Underbelly.

"I don't mind them telling the truth about me, but telling lies and painting me out like some d***head who is brain-dead, well that's just bull***t," he wrote.

"They're having me associating with people I've never met before such as Alphonse. They also have me committing crimes that I've never even been suspected of - what a load of crap."